The use of portable data processing systems has increased significantly in recent years. In addition to so called “laptop” and “tablet” computers, there is a growing popularity in handheld data processing devices, often called a “personal digital assistant” or “PDA.” All of these devices are capable of storing a significant amount of user data, including calendar, address book, tasks and numerous other types of data for business and personal use. Most handheld data processing devices have the ability to connect to a personal computer for data exchange, and many are equipped for wireless communications using, for example, conventional email messaging systems. Depending upon the user's needs much of this data can be highly sensitive in nature, especially in a government, military or commercial context.
Portable data processing systems are typically password protected. However, in the hands of a technically sophisticated individual with malicious intent, there are ways to obtain the data stored in memory in such a device if the data is not encrypted. Accordingly the data stored in persistent memory is typically encrypted using an encryption key. This requires that the same encryption key used to encrypt the data be used to decrypt the data.
In any data storage systems there is a possibility that over time, or because of an event, a portion of the memory will fail. The failure may reveal itself as a single bit error, multiple word errors, or possibly a complete memory failure. When the memory is used to store an encryption key, even a single bit error can corrupt the key sufficiently to render it useless. Should this occur, then the entire volume of data encrypted with the corrupted key becomes undecryptable, and as a result is lost. To prevent this data loss, an uncorrupted encryption key must be available at all times.